1. Field of the Invention
The present invention relates to a tape cartridge having an improved structure for driving a tape reel, a tape reel driving structure, and a tape drive that rotationally drives a tape reel of a tape cartridge.
2. Description of Related Art
Several types of reel driving structures exist wherein a tape reel in a tape cartridge is rotationally driven on a drive shaft of a tape drive in a state in which the tape reel is engaged and coupled with the drive shaft, thereby winding in or feeding out recording tape wound upon the tape reel. Two types of reel driving structures of this kind are known. The first is a type wherein a reel hole is provided within a boss of the tape reel and a drive shaft is fitted into the reel hole, as represented by audio and video tape cartridges (called a “peripheral face coupling type”). The second is a type wherein the end face of a drive shaft couples with the bottom surface of a boss of the tape reel, the two engaging via engaging teeth in gear form, as represented by a single-reel type tape cartridge (called an “end-face coupling type”) (see patent reference 1: JP 2004-273014A (paragraph 0035, FIG. 3)).
According to the peripheral face coupling type reel driving structure, the drive shaft is fitted into the reel hole, and thus a rotational force of the drive shaft can be transmitted reliably. However, clearance is allocated between the drive shaft and the reel hole in an amount sufficient for performing the operation of engaging the drive shaft with the reel hole to be performed in a smooth manner. Accordingly, there is a problem that it is easy for the center of the tape reel and drive shaft to become offset in the radial direction while being driven, and furthermore, a delay in operation equal to the amount of clearance arises when repeatedly starting and stopping the driving process. In the state in which the center is offset as mentioned here, it is not possible to avoid a variance in the speed of feed-out and take-up of recording tape during a revolution of the tape reel, which can easily result in variance in the tape forwarding speed within the tape drive, miswinding when taking up tape, and so on.
According to the end-face coupling type reel driving structure, the end face of the drive shaft is caught by the bottom wall of the tape reel boss, and the two are engaged via engaging teeth in gear form; therefore, unless all engaging teeth are in a properly interlocked state, the tape reel cannot be horizontally supported by the drive shaft. If the tape reel is rotated while the center axis of the reel is in this kind of tilted state, the reel flange will rise and fall during rotation; accordingly, it is impossible to prevent the path of movement of the recording tape from shifting up and down. Therefore, the tracking operation of a read/write head in the tape drive is delayed, or tracking is rendered impossible, when tracing signal tracks recorded onto the recording tape; as a result, reading/writing of the recorded signal cannot be carried out in a stable manner. Reading/writing of the recorded signal in a stable manner is particularly impossible in the case where the recording density of the recording tape is high and the recorded signal is read/written at high speed. There are also situations where miswinding occurs when taking up the recording tape into the tape reel, resulting in the tape edge being marred.
With the tape cartridge according to patent reference 1, a magnet is disposed on the end face of the drive shaft, and an iron-based adhesive plate is disposed on the bottom wall of the tape reel boss, making it possible for the top face of the drive shaft and the bottom wall of the tape reel to tightly adhere to one another. However, there is a problem that as long as all coupling teeth are not properly interlocked with one another, it is impossible to prevent the tape reel from tilting, and impossible to horizontally support the tape reel with the drive shaft in a stable manner, even if the drive shaft and tape reel are tightly coupled through the magnetic effect arising between the magnet and the adhesive plate.